Sample for Strands AgentCore tool search plugin.

The [AgentCore Tool Search plugin](https://github.com/aws/bedrock-agentcore-sdk-python/tree/main/src/bedrock_agentcore/gateway/integrations/strands/plugins/agentcore_tool_search) enables semantic tool discovery for Strands Agents using [Amazon Bedrock AgentCore Gateway](https://docs.aws.amazon.com/bedrock-agentcore/latest/devguide/gateway-using-mcp-semantic-search.html). It allows agents to dynamically load only the relevant tools for each invocation by deriving user intent from conversation history, even when hundreds of tools are registered on the gateway.

Need sample to demonstrate usage of this plugin. I will be creating a PR into 'agentcore-samples/03-integrations/gateway'

Start by reading the AgentCore Tool Search plugin in src/bedrock_agentcore/gateway/integrations/strands/plugins/agentcore_tool_search and the linked AgentCore Gateway semantic-search guide. Add a sample under agentcore-samples/03-integrations/gateway that demonstrates the plugin with Strands Agents; done means the sample clearly shows semantic tool discovery and can be run as documented.

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